The present invention relates to a bookbinding system and a bookbinding method for covering a sheet bundle with a cover sheet and forming a booklet.
An electrophotographic image forming apparatus has a high-speed performance, a multi-function, and a network function and is connected to a large capacity sheet feeding device and a large capacity stacker, thus finds wide applications as a printing press.
Further, as a bookbinding process, a one for covering one sheet bundle composed of stacked printed sheets with a cover sheet in a U-shape and forming a booklet is known.
When using the image forming apparatus as a printing press, a bookbinding apparatus for bookbinding printed papers is connected to it, thus the processing from printing to bookbinding can be performed by one system in a flowing sequence.
The bookbinding apparatus described in Unexamined Japanese Patent Application Publication No. 2004-209870 is connected to the image forming apparatus for use. In this bookbinding apparatus, the adhesive reservoir and roller move back and forth on the bottom side of the sheet bundle integrally with each other, thereby coat an adhesive on the spine of the sheet bundle. The adhesive feeding unit for feeding a granular adhesive holds the sheet bundle at the standby position of the adhesive reservoir and puts a predetermined amount of the granular adhesive into the adhesive reservoir at the opposite position.
In Unexamined Japanese Patent Application Publication No. 2004-209870, the description does not take the adhesive strength of the adhesive coated on the spine of the sheet bundle into sufficient account.
When bookbinding by coating a heated adhesive on the spine of a sheet bundle and pasting a cover sheet thereon, if a toner image is formed as far as the end of each sheet in the neighborhood of the spine of the sheet bundle, by the heat of the adhesive heated at time of coating the adhesive, the toner image is heated and rises in temperature.
The heated toner image is pasted to the neighboring sheet and tacking is apt to occur. When the tacking occurs, the sheets are hardly separated from each other, and the spread amount of each page is reduced, thus the contents described on the page are almost unreadable. Therefore, when the pages are spread forcibly and the sheets are separated from each other, the sheets are broken, and the image is damaged, thus there is the possibility that the bookbinding quality may be impaired.
When sheets with a toner image formed on one side thereof are stacked on top of each other, the heated toner image is closely adhered to the opposite sheet surface, causing pasting of the sheets.
When sheets with a toner image formed on both sides thereof are stacked on top of each other, the toner image heated on either sheet and the toner image heated on another opposite sheet are adhered closely to each other, causing pasting of the sheets.